Extendible stent apparatus

ABSTRACT

The present invention concerns novel stent apparatuses for use in treating lesions at or near the bifurcation point in bifurcated cardiac, coronary, renal, peripheral vascular, gastrointestinal, pulmonary, urinary and neurovascular vessels and brain vessels. More particularly, the invention concerns a stent apparatus with at least one side opening which may further comprise an extendable stent portion laterally extending from the side opening and at least partly in registry with the wall of the side opening. Devices constructed in accordance with the invention include, singularly or in combination, a main expandable stent comprising at least one substantially circular side opening located between its proximal and distal end openings, which side opening may further comprise an expandable portion extending radially outward from the edges of the side opening; and a branch stent comprising proximal and distal end openings and which may further comprise a contacting portion at its proximal end, and which may optionally be constructed to form either a perpendicular branch or a non-perpendicular branch when inserted through a side opening of the main stent. The stents of the invention are marked with, or at least partially constructed of, a material which is imageable during intraluminal catheterization techniques, most preferably but not limited to ultrasound and x-ray.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] The present invention is a regular filing which claims benefitunder 35 USC §119(e) from U.S. Provisional Patent Application Nos.60/088,301, filed Jun. 05, 1998; and is a continuation-in-part of PCTPatent Application WO 99/00835, filed Jan. 14, 1998; the disclosures ofwhich are incorporated herein in their entirety for all purposes.

BACKGROUND OF THE INVENTION

[0002] A type of endoprosthesis device, commonly referred to as a stent,may be placed or implanted within a vein, artery or other tubular bodyorgan for treating occlusions, stenoses, or aneurysms of a vessel byreinforcing the wall of the vessel or by expanding the vessel. Stentshave been used to treat dissections in blood vessel walls caused byballoon angioplasty of the coronary arteries as well as peripheralarteries and to improve angioplasty results by preventing elastic recoiland remodeling of the vessel wall. Two randomized multicenter trialshave recently shown a lower restenosis rate in stent treated coronaryarteries compared with balloon angioplasty alone (Serruys, P W et al.New England Journal of Medicine 331: 489-495, 1994, Fischman, D L et al.New England Journal of Medicine 331: 496-501, 1994). Stents have beensuccessfully implanted in the urinary tract, the bile duct, theesophagus and the tracheo-bronchial tree to reinforce those body organs,as well as implanted into the neurovascular, peripheral vascular,coronary, cardiac, and renal systems, among others. The term “stent” asused in this Application is a device which is intraluminally implantedwithin bodily vessels to reinforce collapsing, dissected, partiallyoccluded, weakened, diseased or abnormally dilated or small segments ofa vessel wall.

[0003] One of the drawbacks of conventional stents is that they aregenerally produced in a straight tubular configuration. The use of suchstents to treat diseased vessels at or near a bifurcation (branch point)of a vessel may create a risk of compromising the degree of patency ofthe primary vessel and/or its branches, or the bifurcation point andalso limits the ability to insert a second stent into the side branch ifthe result of treatment of the primary, or main, vessel is suboptimal.Suboptimal results may occur as a result of several mechanisms, such asdisplacing diseased tissue, plaque shifting, vessel spasm, dissectionwith or without intimal flaps, thrombosis, and embolism.

[0004] The risk of branch compromise is increased generally in twoanatomical situations. First, a side branch may be compromised whenthere is a stenosis in the origin of the side branch. Second, when thereis an eccentric lesion at the bifurcation site, asymmetric expansion cancause either plaque shifting or dissection at the side branch origin.There are reports of attempts to solve this problem by inserting aballoon into the side branch through the struts of a stent deployed inthe main branch spanning the bifurcation point; however, this techniquecarries the risk of balloon entrapment and other major complications(Nakamura, S. et al., Catheterization and Cardiovascular Diagnosis 34:353-361 (1995)). Moreover, adequate dilation of the side branch islimited by elastic recoil of the origin of the side branch. In addition,insertion of a traditional stent into a main vessel spanning a thebifurcation point may pose a limitation to blood flow and access to theside branch vessel. The term “stent jail” is often used to describe thisconcept. In this regard, the tubular slotted hinged design of thePalmaz-Schatz intracoronary stent, in particular, is felt to beunfavorable for lesions with a large side branch and is generallybelieved to pose a higher risk of side branch vessel entrapment wherethe stent prevents or limits access to the side branch. Id.

[0005] One common procedure for intraluminally implanting a stent is tofirst open the relevant region of the vessel with a balloon catheter andthen place the stent in a position that bridges the treated portion ofthe vessel in order to prevent elastic recoil and restenosis of thatsegment. The angioplasty of the bifurcation lesion has traditionallybeen performed using the “kissing” balloon technique where twoguidewires and two balloons are inserted, one into the main branch andthe other into the side branch. Stent placement in this situationrequires the removal of the guidewire from the side branch andreinsertion through the stent struts, followed by the insertion of aballoon through the struts of the stent along the guidewire. The firstremoval of the guidewire poses the risk of occlusion of the side branchduring the deployment of the stent in the main branch.

[0006] In general, when treating a bifurcation lesion using commerciallyavailable stents, it is important to cover the origin of the branchbecause if left uncovered, this area is prone to restenosis. In order tocover the branch origin, conventional stents inserted into the branchmust protrude into the lumen of the main artery or vessel from thebranch (which may cause thrombosis, again compromising blood flow).Another frequent complication experienced when stenting bifurcatedvessels is the narrowing or occlusion of the origin of a side branchspanned by a stent placed in the main branch. Additionally, placement ofa stent into a main vessel where the stent partially or completelyextends across the opening of a branch makes future access into suchbranch vessels difficult if not impossible. As a result, conventionalstents are often placed into the branch close to the origin, butgenerally not covering the origin of the bifurcation.

[0007] Lastly, conventional stents are difficult to visualize during andafter deployment, and in general are not readily imaged by usinglow-cost and easy methods such as x-ray or ultrasound imaging. Whilesome prior art balloon catheters (and not stents) are “marked” at theproximal and distal ends of the balloon with imageable patches, fewstents are currently available which are marked with or which are atleast partly constructed of, a material which is imageable by currentlyknown imaging procedures commonly used when inserting the stents into avessel, such as ultrasound or x-ray imaging. The invention described inthis Application would not work with endoscopy as currently used as animaging method due to size limitations, but future advances in limitingthe size of endoscopic imaging devices may in the future make endoscopicimaging compatible with the stents of the invention.

[0008] Accordingly, there is a need for improved stent apparatuses, mostparticularly for applications within the cardiac, coronary, renal,peripheral vascular, gastrointestinal, pulmonary, urinary andneurovascular systems and the brain which 1) completely covers thebifurcation point of bifurcation vessels; 2) may be used to treatlesions in one branch of a bifurcation while preserving access to theother branch for future treatment; 3) allows for differential sizing ofthe stents in a bifurcated stent apparatus even after the main stent isimplanted; 4) may be delivered intraluminally by catheter; 5) may beused to treat bifurcation lesions in a bifurcated vessel where thebranch vessel extends from the side of the main vessel; and 6) is markedwith, or at least partly constructed of, material which is imageable bycommonly used intraluminal catheterization visualization techniquesincluding but not limited to ultrasound or x-ray.

SUMMARY OF THE INVENTION

[0009] The present invention concerns novel stent apparatuses formethods, and kits use in treating lesions at or near the bifurcationpoint in bifurcated vessels. More particularly, the invention concerns astent apparatus with a main tubular stent body having at least one sideopening which may further comprise an extendable or second stentinserted through the side opening and at least partly in registry withthe wall of the side opening.

[0010] As used herein, the term “vessel” means any body lumen or tubulartissue within the cardiac, coronary, renal, peripheral vascular,gastrointestinal, pulmonary, urinary and neurovascular systems and thebrain. Devices constructed in accordance with the invention include,singularly or in combination, a main expandable tubular stent bodyhaving at least one side opening (usually substantially circular)located between its proximal and distal end openings, which side openingmay further comprise a radially expandable portion extending laterallyoutward from the edges of the side opening; and an expandable branchsecond stent comprising proximal and distal end openings and which mayfurther comprise a contacting portion at its proximal end, and which maybe constructed to form an angularly variable branched stent apparatuswhen inserted through a side opening of the main stent. The radiallyexpandable portion preferably comprises a plurality of laterallydeployable elements, such as loops, tabs, beams, or the like, attachedor coupled to a peripheral edge of the side opening. Usually, theelements will project inwardly from the periphery into the side hole sothat they may be deployed radially outwardly from the periphery to openin a petal-like fashion. The elements may be formed integrally as partof the tubular body structure, e.g., being formed from the bent wire orband or from the cut tubular structure which defines the stentstructure. Alternatively, they could be formed separately andsubsequently attached by crimping, welding, folding, interferencefitting, etc. Optionally, the expandable portion may be covered with afabric or the entire stent structure membrane to help form thetransition between the main body lumen and the lumen of the secondstent. The stents of the invention are marked with, or at leastpartially constructed of, a material which is imageable duringintraluminal catheterization techniques, most preferably but not limitedto ultrasound and x-ray, preferably being radiopaque.

[0011] In a preferred aspect of the stent design, the side hole will bedefined by a continuous band or pattern of material which defines theperiphery of the side hole. The band may have a circular, oval, or otherregular geometry in which case the width and area of the side hole willremain generally constant as the stent is expanded. Alternatively, thecontinuous band may comprise discontinuities over its length so that thearea and/or width of the side hole may expand together with the stentstructure. Preferably, the continuous band will include inwardlyprojecting loops, fingers, or other protrusions which will define thelaterally deployable elements which project inwardly from the peripheraledge of the side opening. The inwardly projecting loops or otherelements may be overlapping or non-overlapping. The use of overlappinglooped structures maximizes the length of the inwardly projectingelements after they are unfolded and opened inwardly into the sidebranch, as described in more detail below.

[0012] In another aspect of the present invention, a stent for placementin a bifurcated body lumen comprises a main tubular body having a firstend, a second end, and a side opening therebetween. A first portion ofthe main tubular body between the first end and the side hole opens inresponse to a first radially outward pressure, typically provided by anexpansion balloon. A second portion of the main tubular body between theside hole and the second end opens in response to a second pressure,again typically applied by an expansion balloon. By constructing themain tubular body so that the first opening pressure is less than thesecond opening pressure, the stent can have differential openingcharacteristics. That is, by introducing a balloon expansion catheterinto the stent and applying a constant pressure over the entire lengthof the balloon, the first portion of the stent will yield and openbefore the second portion of the stent. The particular embodimentsdescribed below, the first yield pressure will typically be in the rangefrom 1 atmospheres to 10 atmospheres while the second yield pressurewill typically be in the range from 2 atmospheres to 18 atmospheres.Such stent structures may be placed by initially opening and deployingthe first portion, typically the proximal portion on the same side ofthe bifurcation as the deployment catheter, and thereafter positioningthe side hole to align more precisely with the bifurcated secondaryblood vessel. After the proper positioning has been achieved, the secondstent portion can then be opened, conveniently using the same expansionballoon which has been inflated to a higher inflation pressure. Suchstents will typically include the laterally deployable elements disposedaround the side opening, as described above, and will optionally be usedin combination with secondary stents, as described above.

[0013] The stent structures as described previously may combineconventional stent elements, such as serpentine rings, diamond or boxstructures, axial expansion members, and the like. In addition, in orderto provide the differential expansion characteristics, the main tubularbodies of the stents may include axial spine structures which differfrom the remaining portions of the tubular body of the stent. Forexample, the first portion of the stent may have an axial spine whichreadily expands circumferentially. By then providing a spine section onthe second portion of the stent which is more resistant tocircumferential expansion, the desired differential expansion will beachieved. Alternatively, the differential expansion can be achieved byemploying stent patterns which are uniformly easier or more difficult toradially expand over their entire peripheral length. Specific examplesof both structures will be described below.

[0014] The stent apparatuses of the invention offers significant andnovel advantages over prior art stents in that the stents of theinvention 1) can completely cover the bifurcation point of a branchedvessel; 2) can accommodate main and branch stents of differing sizes,thus providing a better fit where the main and branch vessels are ofdifferent sizes or where the main and branch vessels are occluded todifferent degrees; 3) can fit branched vessels where the branch extendslaterally from the side of the main vessel; 4) may be used to treatlesions in one branch of a bifurcation while preserving complete accessto the other branch for future treatment; 5) may be deliveredintraluminally by catheter; and 6) are marked with, or at least partlyconstructed of, material which is imageable by commonly usedintraluminal catheterization visualization techniques including but notlimited to ultrasound or x-ray, but not endoscopy.

[0015] Thus, it is an object of the present invention to provide both adouble-stent apparatus and a single-stent apparatus, each of which maybe used to cover the origin of a bifurcation in a branched vessel.

[0016] Another object of the invention is to provide a single-stentapparatus which may be used to treat only one branch of a bifurcationlesion while leaving access to the second branch unobstructed.

[0017] Additionally, it is an object of the invention to provide a stentapparatus which is itself imageable by methods commonly used duringcatheterization such as x-ray or ultrasound.

[0018] Yet another object of the invention is to provide a bifurcatingdouble-stent device wherein the main stent and the branch stent orstents may be of different sizes.

[0019] Lastly, it is an important object of the invention to provide astent apparatus which may be used to treat bifurcated vessels where thevessel bifurcation extends laterally from the side of the main vessel.

[0020] These objects and other object advantages and features of theinvention will become better understood from the detailed description ofthe invention and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a schematic depiction of the double-stent apparatus ofthe present invention in which both the main stent and the branch stentare fully dilated.

[0022]FIG. 2 is a schematic depiction of the main stent of the apparatusof the invention as deployed, with the side opening in registry with avessel bifurcation point.

[0023]FIG. 3 is a schematic depiction of the branch stent of theapparatus as deployed, with the contacting portion fully expanded tocontact the origin of the bifurcated vessel.

[0024]FIG. 4 is a schematic depiction of the main stent of the apparatusdeployed within a subject vessel, after inflation of a balloon to expandthe main stent to fit the walls of the subject vessel.

[0025]FIG. 5 is a schematic depiction of the double-stent bifurcatingstent apparatus, where the main stent is deployed and showing theplacement of the branch stent apparatus prior to full deployment of thebranch stent.

[0026]FIG. 6a depicts initial placement of the main stent of thebifurcating stent apparatus into the vessel, along with the insertion ofa guidewire and stabilizing catheter for placement of the branch stentinto the branch vessel of the subject.

[0027]FIG. 6b is a schematic depiction showing the main stent of theinvention expanded by balloon expansion.

[0028]FIG. 6c is a schematic depiction of the deployment of the branchstent over the side branch guidewire, through one of the side openingsin the main stent and into the branch vessel of the subject.

[0029]FIG. 6d is a schematic depiction of the removal of the protectivesheath of the branch stent allowing for full expansion of the contactingportion prior to final placement and deployment.

[0030]FIG. 6e is a schematic depiction of the compressed branch stentpositioned into the branch by the catheter with the contacting portionat least partly contacting the side opening in the main stent, but priorto full expansion of the branch stent.

[0031]FIG. 6f is a schematic depiction of the fully expanded main stentand the fully positioned and expanded branch stent, where the branchstent is being dilated by inflation of a balloon.

[0032]FIG. 6g is a schematic depiction of the fully expanded bifurcatingdouble stent of the invention, positioned into the bifurcation point ina subject vessel.

[0033]FIG. 7 is a schematic depiction of the main stent with optionalexpandable portion, prior to balloon expansion of the expandableportion.

[0034]FIG. 8 is a schematic depiction of balloon expansion of theoptional expandable portion of the main stent to cover a vesselbifurcation point.

[0035]FIG. 9 is a schematic depiction of the main stent with theoptional expandable portion fully expanded to extend laterally from theside opening of the main stent.

[0036]FIG. 10 illustrates a first stent pattern having a side hole anddifferential expansion characteristics in a “rolled out” view.

[0037]FIG. 11 illustrates a second stent pattern having a side hole anddifferential expansion characteristics in a “rolled out” view.

[0038]FIG. 12 illustrates a third stent pattern having a side hole anddifferential expansion characteristics in a “rolled out” view.

[0039] FIGS. 13A-13H illustrate the deployment of any one of the stentsof FIGS. 10-12 in a bifurcated blood vessel or a secondary stent isplaced through the side hole of the main stent.

[0040]FIG. 14A illustrates a fourth stent pattern having a side hole anddifferential expansion characteristics in a “rolled out” view.

[0041]FIG. 14B shows a stent of FIG. 14A with first portion 804protruding outwardly as a flap during stent expansion.

[0042]FIG. 15 illustrates a fifth stent pattern having a side hole anddifferential expansion characteristics in a “rolled out” view.

[0043]FIG. 16 illustrates a sixth stent pattern having a side hole anddifferential expansion characteristics in a “rolled out” view.

[0044]FIG. 17 illustrates a seventh stent pattern having a side hole anddifferential expansion characteristics in a “rolled out” view.

[0045] The rectilinear matrices shown in the drawings are intended toshow the shapes of the surfaces only, and do not illustrate the actualsurface patterns or appearances of the stent apparatuses of theinvention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0046] The bifurcating double-stent apparatus 10 of the presentinvention comprises a generally cylindrical main stent 12 and agenerally cylindrical branch stent 15, which are shown as fully dilatedin a subject main vessel 8 and a subject branch vessel 7, as illustratedin FIG. 1.

[0047] The main stent 12 contains at least one generally circular sideopening 16 located between the proximal end 26 and the distal end 28 ofthe main stent 12 (FIG. 2), which opening is positioned over and inregistry with the opening 48 of a branch vessel in a vessel bifurcation50, as shown in FIG. 2. The stent 12 and the side opening are imagedduring imaging procedures either by constructing the stent of imageablematerials or by placing markers 56 at appropriate locations, such asaround the perimeter of the side opening 16 in the main stent 12, and atthe proximal end 26 and distal end 28 of the main stent, as illustratedin FIG. 4.

[0048] As shown in the embodiment of the invention illustrated in FIG.4, a guidewire 20 is inserted into the vessel 8 prior to insertion ofthe main stent 12, and is used to guide the main stent 12 into positionwithin the vessel 8. Prior to insertion and expansion, the main stent 12is disposed around the distal end of a catheter 48 which may include aninflatable balloon 24. The main stent/catheter apparatus is thenthreaded onto the main guidewire 20 and into the vessel 8. The mainstent 12 is radially expanded by inflation of the balloon 24 until itexpands the walls of the vessel 8, and is thus affixed into place.

[0049] In a second embodiment of the invention, the branch stentapparatus 15 of the present invention comprises a generally cylindricalstent comprising a proximal end 30 and a distal end 32, as shown in FIG.3. The proximal end 30 comprises a contacting portion illustrated hereas extended loops 18, which contacting portion, when expanded, ispositioned within the lumen 58 of the main vessel 8 (FIG. 3) and atleast partially contacting the perimeter of the side opening 16 of themain stent 12. FIG. 4 illustrates the positioning of the main stent 12(without optional contacting portion) in the main vessel 8 as fullyexpanded by inflation of the balloon 24.

[0050] As shown in the embodiments illustrated in FIGS. 4, 5 and 7, theends of the main stent 12 and the expandable branch stent 15 and thecontacting portion 18 are visible during insertion by placing imageablemarkers 56 around the ends of the main 12 and branch 15 stents and thecontacting portion 18 and at the proximal end 30 and distal end 32 ofthe branch stent. Alternatively, the stent may be at least partiallyconstructed of material which is imageable by methods including but notlimited to ultrasound or x-ray imaging (but not endoscopic imaging).

[0051] As shown in yet another embodiment, the stents of the inventionare combined to form a bifurcating double stent as illustrated in FIGS.5 and 6a-g. After insertion of the main stent as described above butprior to expansion of the main stent (FIG. 6a), the branch stent 15 isinserted through a side opening 16 of the main stent 12, a guidewire 36and a stabilizing catheter 44 are inserted through the side opening 16in the main stent 12, and into a branch vessel 7 (FIG. 6a). Thestabilizing catheter 44 is used to place the side opening 16 in the mainstent 12 over the bifurcation point 50 in the bifurcated vessels 7 and 8(FIG. 6a). In the embodiment depicted here, the main stent is thendeployed into position by inflation of the balloon 24 (FIG. 6b). Duringinsertion and prior to dilation of the branch stent, the branch stent 15is disposed around the distal end of a branch catheter 54 which mayoptionally include an inflatable balloon 25, and the contacting portion18 of the branch stent 15 is held in a collapsed position by aprotective sheath 34, as shown in FIG. 6c.

[0052] In the bifurcating double-stent apparatus 10 of the invention,once the main stent 12 is dilated and the stabilizing catheter 44 (asshown in FIG. 6b) is removed, the branch stent 15 is inserted over thebranch guidewire 36 and through the opening 16 of the main stent 12substantially as shown in FIG. 6c, and affixed in place by withdrawal ofthe protective sheath 34 (FIG. 6d) and insertion of the branch stent 15until it at least partially contacts the perimeter of the opening 16 ofthe main stent 12 by the expansion of the contacting portions 18 whichare positioned at the proximal end 30 of the expandable stent, as shownin FIG. 6e. The branch stent 15, once positioned in the branch vessel 7,may be then fully expanded by the balloon 25, as shown in FIG. 6f. Theangle at which the optionally expandable branch stent 15 is affixeddepends upon the vessel structure into which the bifurcating stentapparatus 10 is inserted. All catheters, and guidewires are thenwithdrawn from the subject vessels, leaving the main stent 12 throughwhich the branch stent 15 is inserted into the branch vessel 7, forminga bifurcated stent 10 (FIG. 6g).

[0053] As illustrated in FIGS. 6a-6 g, the main stent 12 is deployedprior to the branch stent 15. This is the presently preferred order ofdeployment. It will be possible, however, in some circumstances todeliver the branch stent 15 prior to the main stent 12. In such cases,the branch stent 15 will be deployed with the contacting portions 18opened directly against the inner wall of the main blood vessel. Themain stent 12 will then be positioned over the contacting portions 18 ofthe branch stent 15 and firmly expanded thereagainst. A sheath orexpansion balloon can be used to properly align the side opening 16 ofthe main stent 12 with the opening within the contacting portion 18 ofthe branch stent 15.

[0054] In the embodiment shown in FIGS. 7-9, the main stent 40 withexpandable portion 38 is positioned within the vessel 8 by theguidewires 20 (FIG. 7), and affixed in place by radial expansion of themain stent 40, most particularly by inflation of the balloon 25 (FIG.8). The main stent is positioned so that the opening 16 is directly overthe bifurcation point 50 in the subject vessels 7 and 8 (FIG. 7 and 8).In order to aid such positioning, a side branch guidewire 36 and astabilizing catheter 44 (as depicted in FIG. 7) are also insertedthrough the opening 16 of the main stent 40 and through the expandableportion 38 and into the branch vessel 7 (FIG. 8).

[0055] The optional expandable portion 38 of the main stent 40 is thenexpanded radially and in an at least partially perpendicular manner tothe sides of the main stent side opening 16 (FIG. 8). In the embodimentillustrated in FIGS. 7 and 8, a balloon 25 is deployed along the sidebranch guidewire 36 through the expandable portion 38, and inflateduntil the expandable portion is fully expanded into the branch vessel 7to cover the bifurcation point 50 of the branched vessel, as illustratedin FIG. 8. In order to extend the expandable portion 38 into the branchvessel 7, a balloon 25 disposed around a branch catheter 54 which isthreaded along the side branch guidewire 36, through the main stent 40,through the opening 16 and expandable portion 38, and into the subjectbranch vessel 7 as shown in FIG. 8. The expandable portion 38 is thenextended into the branch vessel 7 by inflation of the balloon 25, whichpushes the expandable portion 38 outward radially and lateral to theside opening, into the branch vessel 7 (FIG. 8). Once all catheters andballoons are withdrawn, the expandable portion 38 is arrayed in lateralorientation to the sides of the opening 16 in the main stent 40, andsurrounding the opening 16 into the vessel branch (FIG. 9). Theguidewires 20 and 36 are then withdrawn from the main and branchvessels.

[0056] The expandable portion 38 is illustrated as a plurality ofelements which are attached to the peripheral edge of the side opening16. The elements project radially inwardly into the side opening andthus lie within the cylindrical envelope of the tubular main stent 40prior to deployment, as shown in FIG. 7. The elements are opened byoutward lateral deflection, typically using a balloon catheter, asillustrated in FIG. 8. The deflected elements both traverse thetransition between the stent and the lumen of the branch vessel and alsoserve as an anchor for subsequent placement of the second stent.

[0057] In the double stent apparatus of FIG. 5 and in the main stentwith expandable portion illustrated in FIGS. 7 and 9, the main stent aswell as the expandable portions may be constructed at least partially ofand/or coated or plated with an imageable material or marked withimageable markers 56 at suitable locations, including around theperimeter of the side openings of the main stent and at the ends of theexpandable portions. In the differentially expandable stent structuresof FIGS. 10-12 (described below), a distal portion may be radiopaquewith the remainder being radiolucent. Suitable imageable materials areradiopaque, such as gold, tungsten, and the like.

[0058] When reinforcing a bifurcated vessel where both branches of thevessel require reinforcing, either 1) the single main stent with theexpandable portion is used whereby the expandable portion extends intothe vessel branch at least partly covering the origin of thebifurcation, which may be used alone or in combination with anyconventional stent; or 2) the main stent without the expandable portionand at least one branch stent with contacting portion are used, thebranch stent placed to extend through at least one side opening of themain stent into at least one branch vessel, wherein the branch stent isat least partially in registry and contacting the edge of the sideopening through which it extends. The branch stent extends laterally atvarying angles to the side opening of the main stent. When treating abifurcated vessel where the area to he treated spans the bifurcation andunobstructed access to the unstented vessel is required, the main stentmay be used either with or without the expandable portion, wherein atleast one side opening is placed over the bifurcation point.

[0059] The stent apparatus of the invention may be constructed from anynon-immunoreactive material, including but not limited to any of thematerials disclosed in the prior art stents which are incorporatedherein by reference. It is intended that the stent apparatuses of theinvention may further be at least partially constructed of, or marked atcertain points with, a material which may be imaged, most particularlybut not limited to by x-ray and ultrasound.

[0060] The stents of the invention may be deployed according to knownmethods utilizing guidewires and catheters, which are then withdrawnfrom the subject following deployment of the stents. The subject stentsmay be self-expanding to conform to the shape of the vessel in whichthey are deployed, or they may be expanded utilizing balloon catheters,or by any other method currently known or developed in the future whichis effective for expanding the stents of the invention. It iscontemplated that prior to deployment the stents will be in a collapsedstate, and will require either mechanical expansion (such as, forexample, by balloon expansion) upon deployment or, for self-expandingstents, will require that the stent be confined to the catheter untildeployment by, for instance, a retractable sheath, in which the sheathis removed during deployment and the stent self-dilated. The stents ofthe invention and the optional expandable portion of the main stent ofthe invention expand radially from their longitudinal axis, lateral tothe side opening of the main stent. Other methods of dilation of thestents of the invention may exist, or may become available in thefuture, and such methods are contemplated as being within the scope ofthis invention.

[0061] Referring now to FIGS. 10-12, the present invention furtherprovides stent structures having differential radial expansioncharacteristics. In particular, tubular stent structures having sideholes, generally as described above, are configured so that a portion ofthe stent on one side of the side hole will expand at a different yieldor threshold force than a portion of the stent on the other side of theside hole. Such different yield forces or pressures may be achieved in avariety of ways. For example, referring to FIG. 10, a stent 100 isillustrated in a “rolled out” view, i.e., the tubular stent is brokenalong an axial line and then rolled out in the resulting pattern shownin the Figure. The pattern shown in FIG. 10 is prior to expansion. Thestent 100 includes a side hole 102 defined by a continuous band 104having a plurality of loops 106 projecting into the open interior of theside hole. The loops 106 are an integral part of the band 104 and will,prior to expansion or opening, lie within the cylindrical envelope ofthe tubular body of the stent. The first portion 110 of the stent lieson one side of the side hole 102 and is defined by a plurality ofserpentine rings 112. The serpentine rings are joined by axial expansionspring structures 114 so that the stent may be bent as it is introducedand/or deployed. A second portion 120 of the stent 100 is formed on theother side of side hole 102. The second portion is also defined by theplurality of serpentine rings 122 which are generally similar instructure to the rings 112 of the first portion 110. Each of theportions 110 and 120, however, include an axial spine 130 and 132. Theaxial spine 130 of the first portion 110 comprises simple W-shapedstructures including outermost struts 134 which open at a relatively lowexpansion force on the adjoining hinge regions. In contrast, the axialspine 132 of the second portion 120 comprises box elements 138 whichrequire a greater expansion force to open. Thus, in deployment, thefirst portion 110 will yield first to allow partial opening before thesecond portion 120 begins to open.

[0062] A second stent structure 200 having differential expansioncharacteristics is illustrated in FIG. 11. A side hole 202 is formedfrom a continuous band of material, generally as described for FIG. 10.A first portion 204 and second portion 206 of the stent each comprise aplurality of serpentine ring structures 208 and 210, respectively. Whilethe specific geometries differ, the structures of stents 100 and 200 aregenerally the same, except for axial spine portions 220 and 230 in thefirst portion 204 and second portion 206, respectively. The first spineportion 220 comprises a simple U-shaped loop having a pair of strutsjoined by a simple C-shaped hinge region. The spine 220 will thus openat relatively low expansion forces. In contrast, the axial spine 230 ofthe second portion 206 comprises a serpentine element which allows foraxial expansion but does not permit radial expansion at all. Thus, thefirst portion 204 will begin opening at much lower expansion forces orpressures than will the second portion 206.

[0063] A third concept for providing differential expansion isillustrated in FIG. 12. Stent 300 comprises a side hole 302 (which isshown in halves in the illustration), a first portion 304, and a secondportion 306. The first portion 304 and second portion 306 each compriseserpentine rings 308 and 310, respectively. Differential expansion,however, is not achieved by providing a particular axial spine region,but rather by having different characteristics in the serpentine rings308 and 310. The serpentine rings 308 have axially aligned struts joinedby simple hinge regions. The length of the struts is relatively long(compared to those in the second portion 306 as described below) so thatthe rings will open at a lower expansion pressure or force. Theserpentine rings 310 of the second portion 306 have relatively shortaxial struts defined by hinge regions each having two bands. Suchstructures require a greater expansion force than do the serpentinerings 308 of the first portion.

[0064] A fourth concept for providing a differential expansion stent isillustrated in FIGS. 14A and 14B. Stent 800 comprises a side hole 802which is defined by parallel struts 804 and curved struts 806. Struts804 can be expanded radially outwardly, forming a flap during stentexpansion as illustrated schematically in FIG. 14B. Accordingly, struts804 can be positioned to support the proximal section of a bifurcatedvessel during stent expansion. As described above, portion 805 of stent800 will preferentially expand at a different rate than portion 807 ofstent 800.

[0065] A fifth differential expansion stent 900 is illustrated in FIG.15. Stent 900 has a side hole 902 which is tear-drop shaped, offeringthe advantage of easier expansion of the strut members 904 duringdifferential expansion the stent 900.

[0066] A sixth differential expansion stent 920 has side opening 922.Wavy bridges 924 connected to horizontal strut members 926 are adaptedto provide superior flexibility in axial bending. Wavy bridges 928around the perimeter of side opening 922 operate to provide axialflexibility about the side hole 922.

[0067] A seventh differential expansion stent 940 is shown in FIG. 17.Stent 940 has a side hole 942 which is oval in shape and comprised ofpair of long struts 944 and 946 at opposite sides of side opening 942 asshown. Wavy bridges 948 facilitate axial bending.

[0068] It will be appreciated that numerous other specific designs maybe provided for differential expansion. What is important to the presentinvention, however, is that at least a portion of the stent on one sideof the side hole, usually the entire length of the stent on that side ofthe hole, will be able to open prior to opening of the stent on theother side of the side hole. Preferably, the first portion of the stentwill open at a balloon expansion pressure in the range from 1atmospheres to 10 atmospheres, while the second portion of the stentwill open in response to a balloon expansion pressure in the range from2 atmospheres to 18 atmospheres.

[0069] Referring now to FIGS. 13A-13H, deployment of stent 100 will bedescribed. While reference is made to stent 100, it will appreciatedthat the same method could be used as well with either of stents 200 or300. Initially, a pair of guidewires GW1 and GW2 will be deployed in thelumen, typically a bifurcated blood vessel, so that guidewire GW1extends through the main lumen of the main vessel past the ostium O ofthe branch vessel BRV. The second guidewire GW2 will be advanced throughthe lumen of the main vessel and into the lumen of the branch vesselBRV, as illustrated in FIG. 13A. The stent 100 will then be introducedover the guidewires on a delivery catheter 400 having an expansionballoon 402, where the stent is crimped over the expansion balloon. Asheath 404 is disposed in the second portion 120 of the stent with itsdistal tip (not shown) terminating immediately before the side opening102. The assembly of the stent 100, delivery catheter 400, and sheath404 will be delivered with the first guidewire GW1 passing through aguidewire lumen of catheter 400 and the second guidewire GW2 passingthrough the sheath 404, as illustrated in FIG. 13B. Initial alignment ofthe side hole 102 of stent 100 is achieved by advancing the stent sothat the side hole lies close to the ostium O.

[0070] After an initial rough alignment is achieved, the balloon 402 isinflated to an initial inflation pressure which opens the first portion110 but which leaves the second portion 120 in its substantiallyunexpanded configuration, as shown in FIG. 13C. Such partial openingallows the sheath 404 to be advanced over guidewire GW2 to better alignthe side hole with the branch vessel BRV, as shown in FIG. 13D. Thesheath provides much greater stiffness than the guidewire, permittingmanipulation of the partially deployed stent 100 to achieve the betteralignment.

[0071] Referring now to FIG. 13E, after alignment is achieved, theballoon 402 will be inflated to a greater inflation pressure to open thesecond portion 120 of the stent 100 as well. A balloon catheter can thenbe advanced over the second guidewire GW2 so that balloon 502 can beexpanded within the side opening 102 to open the loops 106, asillustrated in FIG. 13F. In many cases, this will be sufficientdeployment for the stent where the loops provide the necessary anchoringand transition at the ostium O.

[0072] Optionally, a secondary stent 600 may be introduced asillustrated in FIGS. 13G and 13H. The stent 600 is introduced over aballoon 702 on balloon catheter 700. The final deployment configurationis illustrated in FIG. 13H.

[0073] It is intended that the invention include all modifications andalterations from the disclosed embodiments that fall within the scope ofthe claims of the invention.

What is claimed is:
 1. A stent for placement in a bifurcated body lumenhaving a main branch and a side branch, said stent comprising: a maintubular stent body having a first end, a second end, a lumentherethrough, and a side opening have a plurality of laterallydeployable elements therein.
 2. A stent as in claim 1, wherein theelements are formed as an integral part of the stent body.
 3. A stent asin claim 2, wherein, prior to deployment, the laterally deployableelements are aligned in a tubular envelope defined by the tubular stentbody.
 4. A stent as in any of the preceding claims, wherein the maintubular stent body is resilient so that it may be released fromconstraint for deployment.
 5. A stent as in any of the preceding claims,wherein the main tubular stent body is deformable so that it may beexpanded by a balloon catheter.
 6. A stent as in any of the precedingclaims, wherein at least a portion of the main stent body is radiopaque.7. A stent as in claim 6, wherein at least a portion of the main stentbody surrounding the side hole is radiopaque.
 8. A stent as in any ofthe preceding claims, having a radially compressed configuration,wherein the length is less than 4 cm and the diameter is less than 2 cm.9. A stent as in any of the preceding claims, wherein the side holecomprises a continuous band.
 10. A stent as in claim 9, wherein thelaterally deployable elements are inwardly projecting loops of thecontinuous band.
 11. A stent for placement in a bifurcated body lumen,said stent comprising: a main tubular body having a first end, a secondend, and a side opening between said ends, wherein a first portion ofthe main tubular body between the first end and the side hole opens inresponse to a first radially outward pressure and a second portion ofthe main tubular body between the side hole and the second end opens inresponse to a second pressure, wherein the first pressure is less thanthe second pressure.
 12. A stent as in claim 11, wherein the firstpressure is in the range from 1 atmospheres to 10 atmospheres and thesecond pressure is in the range from 2 atmospheres to 18 atmospheres.13. A stent as in claim 11 or 12, wherein the first portion has a firstaxial spine and the second portion has a second axial spine, wherein thefirst axial spine opens circumferentially to a first force and thesecond axial spine opens circumferentially in response to a secondforce, wherein the first force is less than the second force.
 14. Astent as in claim 11 or 12, wherein the first portion comprisesserpentine rings with a first strut length and the second portioncomprises serpentine rings with a second strut length, wherein the firststrut length is greater than the second strut length.
 15. A stent systemcomprising: (a) a stent as in any of the preceding claims; and (b) asecond stent adapted to fit within and contact the laterally deployableelements of the main tubular stent.
 16. A method for attaching a secondstent to a first stent, said method comprising: expanding a main tubularstent body; and laterally deflecting a plurality of elements disposedabout a side opening on the main tubular stent body.
 17. A method as inclaim 16, further comprising placing a second stent into the side holeso that said second stent engages the laterally deflected element.
 18. Amethod for deploying a stent in a bifurcated body lumen, said methodcomprising: providing a stent having a first portion, a second portion,and a side hole between said portions; expanding a first portion againsta luminal wall segment on one side of the bifurcation; aligning the sidehole with the branch lumen; and expanding the second portion on theother side of the bifurcation.
 19. A kit comprising: a stent as in anyof claims 1 to 10; and instructions for use setting forth a methodincluding the following steps: (a) expanding the main tubular stent bodyin a body lumen so that a side hole on the stent body is aligned with abranching body lumen; and (b) laterally deflecting a plurality ofelements disposed about the side opening so that they enter into thebranching body lumen.
 20. A kit comprising: a stent system in claim 9;and instructions for use setting forth a method including the followingsteps: (a) expanding the main tubular stent body in a body lumen so thata side hole on the stent body is aligned with a branching body lumen;(b) laterally deflecting a plurality of elements disposed about the sideopening so that they enter into the branching body lumen; and (c)placing the second stent into the side hole so that said second stentengages the laterally deflected plurality of elements.
 21. A kitcomprising: a stent as in any of claims 11-14; and instructions for usesetting forth a method comprising the following steps: (a) expanding afirst portion against a luminal wall segment on one side of thebifurcation; (b) aligning the side hole with the branch lumen; and (c)expanding the second portion on the other side of the bifurcation.